Telephone system



June 2, 9 i I 1,540,062

" A. H..DYSON TELEPHONE SYSTEM Filed July 20, 1905 7 Sheets-Sheet 1 Wqnassas=- I IHVEHTOR=- June 1925- 1,540,062

A. H. DYSON TELEPHONE SYSTEM Filed July 20, 1905 7 Sheets-Sheet 2 \lvi nassasw THVENTORI- A. H. DYSON TELEPHONE SYSTEM v Sheefis-Sheet Filed July 20 1905 I l I lflllHl THvEn oP- WITNESSES2- June 2, 1925. 1,540,062

A H. DYSON TELEPHONE SYSTEM Filed July 20, 1905 '7 Sheets-Sheet 4 Imam-cam gw M $93 9% N be v A. H. DYSON TELEPHONE SYSTEM 7| Sheets-Sheet 5 Filed July 20, 1905 lll InvEn oRF IWITHESSESR 1,540,062 A. H. DYSON TELEPHONE SYSTEM 7 sheets-sheet a June 2,

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June 25 1925.

A. H. DYSON .TELEPHONE SYSTEM Filed July 20 1905 7 Sheets-Sheet 7 IHVEHTORI- Patented June 2, 1925.-

UNITED STATES PATENT OFFICE.

ALr tED H. DYSON, OF CHICAGO, ILLINoIs, AssIeNOn BY MESNE ASSIGNMENTS, TO KELLOGG swI'ronnoAnna SUPPLY COMPANY, A CORPORATION or ILLINOIS.

TELEPHONE SYSTEM.

Application filed m 20,

To all whom it may concern.

Be it known that I, ALFRED H. DYSON, a citizen of the United States, resident of Chicago, county of Cook and State of Illinois, have invented new and useful Improvements in Telephone Systems, of which the followingis a specification.

My invention relates to telephone systems inwhich the interconnection of subscribers lines is accomplished by means of automatic switches at the exchange, responsive to callingmechanism operated by subscribers. My invention includes novel central office circuit arrangements for connecting for conversation subscribers whose lines terminate in the same. exchange. It also includes a circuit arrangement adapted to be used for trunking purposes between exchanges, and. providesmeans whereby subscribers in different exchanges may have their lines interconnected for conversation automatically, each trunk circuit between exchanges consisting of two conductors only.

My invention further includes a machine switch, embodying certain novel arrangements of mechanical parts. Machines of this type may be operated in connection with certain portions of the circuit arrangements, as hereinafter pointed out in the detailed description.

Referring to the drawings, Figure 1 is an illustration of the machine switch of my invention.

Figure 1, Figure 1", Figure 1 Figure 1,

' Figure 1 and Figure 1' illustrate details of the switch shown in Figure 1. t

Fig. 2 illustrates in diagrammatic form a subscribers telephone line extending from a substation to the exchange and there connected to an automatic switch with which is shown associated the circuits of a first selector.

Fig. 3 illustrates similarly the circuits of a second selector and a battery control circuit.

Fig. 1 illustrates similarly the circuits of a connector and a second telephone'line provided with its automatic switch.

Fig. 5 illustrates circuits of a second selector and a. battery control circuit different from that of Fig. 3.

Fig. 6 illustrates a trunk circuit and'a bat- 1905. Serial No. 270,492.

its being attached to motor-spring 37. Upon the lower portion of shaft 1 are rigidly mounted thirty wipers in sets of three, A", A A etc.; B", B etc.; C C", etc., those having the same coefficient constituting a set.

These wipers are insulated from each other and are disposed radially by sets, with respect to the shaft. Adapted to'be engaged by these wipers are thirty sets, or curved rows, of immovable contacts, of which a sectional view is shown in Figure 1, each row being provided with a common strip extending beneath and parallel to it. The said contacts are mounted in three banks in vertical and horizontally curved rows.

A top view of the wipers and contact banks is shown in Figure 1', a being the common terminal. When shaft 1 is caused to rotate from left to right, wiper A passes over the horizontal curved row of contacts a-. tance such that it assumes the position of wiper A as-shown in Figure 1, wiper A is in a position, with respect to the vertical edge of the contact bank, similar to that of wiper A, shown in the illustration. shaft continuing to revolve, wiper A passes over the lowest curved row of contact points a \Vhen the said wiper has passed over the last of said contact points, the shaft eon-.

When the said wiper has revolved a dis- The tinuing to revolve, wiper A engages the first contact at the left of row a and when the said wiper has left the row, wiper A begins passing over'the contacts of its appropriate row. It will be seen that one com'plete revolution of the shaft 1 will cause each immoverating the switch, a number of primaryiotary movements of the shaft are allowed, depending upon the level of immovable con- In accordance with my invention, in op-.;-

shaft 1;

tacts with which it is desired to connect. Each of these first movements is suflicient to move a set of wipers entirely across its respective rows of contacts. I When the desired set of wipers is, in this manner, brought,

with respect to its contact banks, to a position corresponding to that of wiper A", as shown in Figure 1, a number of secondary rotary movements of the shaft in the same direction are allowed, to move the said de sired set of wipers from contact to contact of its rows, each movement causing the wipers to close contact between successive contacts and their commons, the movement of the wipers being arrested when the proper contacts are engaged by them.

To secure the return of the switch to normal, the shaft is allowed to complete the revolution upon which it has been started, its movement being arrested as soon as the revolution is c'ompleted' Upon such completion, apparatus is automatically brought into play to cause spring 37 to be wound up, preparatory for a further use of the switch. It will be noted that each time the switch is operated and returned to normal, each contact in the different banks is wiped by its appropriate wiper, and this is believed to be a new and valuable feature of a switch of this character, inasmuch as the accumulation of dust upon contacts and wipers is prevented and they themselves kept, at all times, bright and clean.

The movements of the shaft are controlled 1 in the following manner, reference being had to Figure 1: one or more impulses of current are first caused to flow through mag net 8, depending uponthe contact levels to be selected. Each lmpulse of current causes the attraction and release of armature 9. Mounted upon shaft 1 is a disk 4, having a single tooth in its periphery which, as shown in the illustration, is engaged by detent 15, preventing movement of the shaft. Arm 10 mounted upon armature 9 (the end of which is illustrated as broken) extends downward so as to overlap arm 14 mounted upon armature 12, its lower end being on a level with the lower end of arm 14, this being shown complete in Figure-1. The first attraction of armature 9 causes arm 10 to press against the projection shown upon detent 15, causing the said detent to move out of engagement with the tooth upon disk 4, so thatthe detent no longer restrains movement of Mounted upon armature 9 is detent 5 which, upon the attraction of the armature, presses against the circumference of circular ratchet wheel2 rigidl attached to shaft 1, arresting movement 0 the shaft when it has rotated the distance from one tooth of ratchet wheel 2 to the next by engaging said next tooth. Successive attractions and releases of armature 9 permit movements as described, and the extent of revolve one step from left to right.

these movements is so guaged as to bring successive sets of wipers to positions in front of, but not engaging, the first contacts of their respective levels.

Figure 1 is a top view of. ratchet wheel 2, detent 5 being shown in the normal position.

3. is a second ratchet wheel rigidly attached to shaft 1, its teeth being so spaced that successive movements, as determined vthereby, allow movements of the wipers from contact to contact only. Normally engag ng the said ratchet wheel 3, is detent 7, havmg upon it a projection adapted to be engaged by arm 10 upon armature 9 with each attraction of the said armature, and

moved out of engagement with ratchet wheel 3 and so held as long as the armature is attracted. With each release of armature 9, detent 7 engages a tooth of wheel 3 and arrests rotation of the shaft.

The rows having been selected in the manner described, one or more impulses of current are now caused to flow through magnet 11, depending upon the proper contacts in the rows. Each impulse causes the attraction and release of armature 12 which controls detent 6 in a manner generally similar to that in which detent 5 is controlled by magnet 8, the shaft being permitted to rotate one step for each impulse. Detent 7, with each energization of magnet 11, is causedto release ratchet wheel 3 by the operatlon of arm 13; andupon the deenergization of the magnet, again engages the wheel, preventing movement of shaft 1.

Figure 1 is another view of the arrange ment of these parts. Upon armature 12 of magnet 11, is shown arm 14, adapted to cause the retraction of detent 15, should the the saidAvipers into positions where they may be controlled bymagnet 11. In other words, ten impulses 'of current are sent through magnet 8 to bring the zero wipers into operative position, thus constituting a complete revolution and causing engagement of disk 4 by detent 15.

Referring now to Figure 1, when magnet 16 is'energized, pawl 21, pivota-lly associated with its armature 20, moves downward, engaging the next tooth of ratchet wheel 26. When the magnet is de-energized, armature 20 is retracted and awl 21 moves in a vertical direction, causing ratchet wheel 26 to The said ratchet wheel is rigidly attached to ratchet wheel 27 moving the latter with it, and the end of lever 27 is moved out of engagement with the tooth of ratchet wheel 27, previously engaged by it, and rests upon the periphery of the wheel. The said lever being mechanically connected to circuit changing spring 29 as shown, this movement causes the said spring to disengage spring 28 and to engage spring 30. Lever 27 may be mechanically attached to, and cause simultaneous movements of, a plurality of circuit changing springs.

\Vhen magnet 22 is energized, its arma ture 23 is attracted. Pivotally associated with the said armature is pawl 24, engaging a tooth of ratchet wheel 26, the pawl upon the attraction of armature 23 moving toward the left, revolving ratchet wheel 26 one step and thereby moving ratchet wheel 27 into such a position that lever 27 again engages with its end a tooth of ratchet wheel 27, adjacent to that from engagement with which it was moved by the above described operation of pawl 21. This operates to move the circuit changing spring 29 outof engagement with spring 30 and again into engagement with spring 28, its normal position.

The attraction of armature 23 also moved arm 25 toward the left in such manner that an orifice toward its projecting end is caused to slip over and engage the pin shown in the illustration upon'detent 7. In Figure 1", a top view of these parts is shown. When magnet 22 is' de-energized, arm 25 is moved toward the right by the return of armature 23, and reference to Figure. 1 makes clear the manner in which this movement of arm 25 moves detent! out of engagement with' ratchet wheel 3.

The disengagement of. detent 7 in the manner described operates to restore the wipers to normal by allowing a free rotation of the shaft, until detent 15 engages the sin gle tooth of disk 4.

Referring to Figure 1, 31 illustrates (viewing it from in front) an arm of considerable length, extending from the.rear of the switch and engaging, with one edge, a

disk fastened to shaft 1 at all times. VVhen' the shaft isin its normal position, as shown in Figure 1, the edge of arm 31 engages a depression or flattened portion 31 in the periphery of disk 31, as shown in Figure 1 and, in this position the arm 31 engaging the projection shown upon arm'25, holds the i said arm above the pin on detent 7. With the first rotary movement of the shaft, the

edge of arm 31 disengages the depression -mentioned, and rests upon the periphery of the shaft; its end, under these circumstances, being moved to the right so that it no longer supports arm 25 in the position shown in Figure 1. It is retained thus'retracted until the shaft has completed one revolution. When this occurs, its edge again engages the depression in shaft 1 before mentioned, its end moves forward and lifts arm 25' out of engagement with detent 7 in which it was step from left to right. V idly attached to ratchet 41 and moves with placed to release the switch, so that the said detent again engages ratchet Wheel This, it will be noted, occurs at the termination of the release operation before described and simultaneously with the engagement of detent 15 withdisk 4, detent 7 being thereby the left; and when the shaft approaches the completion of its revolution, pawl 39, attached to and moving with pawl 38, engages a tooth of ratchet wheel 41 adjacent to that previously engaged by it. As soon as the revolution of the shaft is completed, pawl 38 engages the off-set in cam 36, its free end moving toward the center of the shaft and retracting pawl 39 to move ratchet 41 one Ratchet 40 is r'igthe latter, the end of spring 43 (see Figure 1*) being moved out of its engagement with a tooth of ratchet 40, which is its normal position, in such a manner that it rests upon the periphery of the said ratchet. Spring 43 is thereby caused to engage spring 42, and

.' this closes circuit through winding magnet 32. The said magnet is arranged in a vibratory circuit, a novel form of circuit break- I er being provided consisting-of disk 46 (see Figure 1) and its associated parts. This circuit breaker is designed to secure a full stroke of the armature of magnet 32 before the magnets circuit is broken. and operates in the following manner: The energizing circuit of magnet 32 passesthrough contact 47- 48. Upon disk 46 is provided adepression 46 engaged by one end of armature 33, and asecond depression 46 adapted to be engaged by lever 46. When armature 33 is attracted, its end, engaging depression 46, moves upward, and as the full stroke of the armature is completed, it impacts upon the upper edge of depression 46. This causesa slight rotary movement of disk 46 from left to right, and lever 46 is thereby caused to the disk reestablishing contact between springs 4 and 48, and causing another energization of the magnet.

Each attraction and release of armature 33 of magnet 32 causes ratchet 34 to be revolved a step from left to right by means of pawl 33, the said ratchet moving independently of shaft 1, and the shaft remaining motionless under these conditions. One end of spring 37 is attached to ratchet 34 and-the movement of freely moving ratchet 34 is in the same direction as the movement of the shaft when the switch is operated. This movement of ratchet 34, 'therefore, operates to wind up the said spring.

Mounted upon ratchet 34 is cam 35 (Fig. 1), its shape being similar to that of cam 36, being provided with an off-set normally engaged by pawl 38. The described winding movement of ratchet 34 movingcam 35 with it, gradually moves pawl 38 to the left;

and when ratchet 34 approaches the completion .of its revolution, pawl 38 causes pawl 39 to engage the next tooth of ratchet 41. When armature 33 has been vibrated a sufficient number of times to causea complete revolution of'ratchet 34, cam 35 will. also have made a complete revolution and pawl 38 again engages its off-set. Pawl 39 then moves to the right and effects a rotary movement of ratchet 41 one step from left to right. It will be noted that this is the second movement of ratchet 41 accomplished in the winding operation, and this second movement operates to bring ratchet 40 in such a position that spring 43 moves from the periphery of the ratchet into engagement with the tooth next to that engaged b it before the winding operation commence his engagement causes sprin 43 to disengage spring 42 and opens t e circuit ofmagnet 32, preventing further operation of the said magnet.

All operating parts of the switch have" now been returned to normal, and energy has been stored for operating the switch a second time. a

While I have especially designed the switch, shown in Figure 1, for use in connection with the circuit arrangements shown at the right of Fig. 2, at the left of Fig. 3, at the left of Fig. 5, at the right of Fig. 6, andwith minor changes in connection with the circuit arrangement shown at the left of Figure 4, the invention of the latter figures is not necessarily confined to the operation of such a machine as I show in Figure 1. ure 1 is generically illustrative of forms'of mechanical movements which different parts of the circuit arrangements, comprised in my invention, may assume. For purposes of reference, I shall designate, b descriptive terms, the prlncipal magnets 1llustrated in Figure 1. When, in the description of the circuit drawings, I come to an electromagnet Fig-- whose work may assume a form similar to that accomplished by a magnet of Figure 1, I shall designate it by the descriptive title. A magnet, having functions similar to magpet 8, may be called a primary magnet.

A magnet, having functions similar to magnet 11, may be referred to as a secondary magnet.

A magnet, having functions similar to 7 magnet 16, may be referred to as a circuitchanging switch magnet.

A magnet, having functions similar to magnet 22, may be referred to as a release magnet.

Referring to the circuit arrangements Figures 2, 3 and 4 placed in the order named with Fig. 2 at the left constitute a first complete dia ram illustrativeof the circuits of the telep one system of my invention. The apparatus included in this single diagram is that necessary for establishing connection between two subscribers lines. In Figure 2, I have illustrated a substation A including a pair of keys 60 and 61 adapted to be used by the subscriber for grounding limbs P and S, respectively, of the telephone line at will. A key 62 is also provided, enabling the subscriber to open the metallic circuit of the substation. Limbs T and S extend 'to the central office and are there connected with an automatic switch individual to the line, which may be called a private switch.

The system, which I have shown in the diagram referred to, may be used to accommodate several thousand subscribers. 'Each subscribers line isprovided with an automatic switch, having circuits similar to those illustrated in Figure 2, and these switches may be conveniently divided into groups of one hundred, each switch including movable'switch arms or wipers such as are designated 82, 98 and 97 in Figure 2, together with a plurality of contacts constituting the multipled terminals of first selector switches. These contacts may conveniently be' disposed in three curved rows, one above the other; those of the upper row, among which contact 80 would be lncluded, being disposed in such manner that successive terminal contacts alternate with permanently roundedcontacts, such as contact 81. ach row or level of contacts is provided with a common strip, such as I have shown at 79, 100* and 99 in Figure 2. These common strips are the true terminals of the circuits of'the private switch, wipers 82, 98 and 97 having themselves no circuit connections, but being arranged so that when the switch is operated, they close cir- 12 cuits between the common strips and the contacts before mentioned. 1

The number of first, selector switches, assigned to a group of one hundred private switches, may vary, depending upon the "$0 til ' in an ordinarily busy exchange.

A first selector switch, circuits of which I have illustrated at the right of Figure 2, is

common for connection to-all subscribers in the exchange.

At the left of Figure 3, I have illustrated the circuits of a second selector switch, such a switch being common for connection to a group of one thousand subscribers lines.

At the left of Figure 4, I have illustrated the circuits of a connector switch, such a switch being common for connection to a group of one hundred subscribers lines,

Generally speaking, a calling subscriber first connects his telephone line through to a first selector switch by operating his private switch. He thereupon operates the first selector switch in such manner that it connects his line through to a second selector switch assigned to the onethousand line group of subscribers lines, among which is included the line of the subscriber whom he is calling. The subscriber then operates the second selector switch in such manner that it connects his line through to a connector switch adapted to be operated to connect his line directly to any line of a one hundred line group of the aforementioned one thou sand line group, among which is the line of the desired subscriber. He then operates the connector switch to connect his line through to the desired subscribers line. The system operates as a multiple trunk system, the principles of which are well known in the art.

Referring to the complete diagram before mentioned, and assuming that subscriber A desires to connect his line with the line of subscriber B, whosenumber is assumed to be 3456, the operation of the system is as follows: Subscriber A first removes the receiver from the switch hook, closing contact Til-72 and establishing a flow of current as follows: from ground at the central office, through contact 6768, through contact (SQ-70. over limb S of the line, returning over limb P, through contact 6364, through the winding of relay 66 to battery 74, energizing relay 66,, which attracts its armatures. This attraction causes a flow of current from ground, through contact 86-87, through contact 7 6-75, through the winding of magnet 90, contact '91 92, to hattery74. Magnet 90 is placed in a vibratory circuit and *will alternately be energized and de-energized as long as relay 66 maintained energized, due to contact 76-75 being closed. Each energization and de-energization of magnet 90 causes shaft 96 to rotate a step, carrying with it. rigidly attached wipers 82, 98 and 97. The first movement of the shaft brings wiper 82 out of engagement with a contact, a multipled terminal of the first selector switch last used by subscriber in establishing a connection, and into engagement with a permanently grounded contact such as 81. Current thereupon flows from ground, through said contact, through wiper 82, through common strip 79, through contact 8384,' through contact 77-78, through the winding of relay 66 to battery 74, locking the said relay and preventing its de-energization by the opening of contact 6768 which occurs as the relay becomes energized.

, The second energization and de-energization of magnet 90 brings wiper 82 into engagement with a contact, the terminal of a first selector switch. Should this switch be already in use, current continues flowing through relay 66 maintaining it energized, the path being traced as follows: from ground, through relay 89 of the private switch then connected with a multipled terminal of the first selector switch, through contact 85-83 of the said private switch, through the common strip of the said switch, its wiper 82, a contact, a multiple of the one which wiper 82 of the private switch of subscriber A just engaged, through the contact engaged by the said wiper to the common strip of the private switch of subscriber A, through contact 83-84 of the said switch, through contact .7 7 7 8, through the winding of relay 66 to battery 74. The windings of relays 66 and 89 are so proportioned that this flow of current is not of sufficient volume to cause relay 89 to atlector switch illustrated in Figure 2, and

that the said switch is idle, circuit through relay 66 is broken, due to the fact that contact 80 is insulated from ground, as appears upon an inspection of Figure 2, in which the first selector switch is shown in itsldle position. Relay 66 becomes de-energized, the retraction of its armature opening the 011'- cuit of magnet 90 at contact 76-75, thereby arresting wipers 82, 98 and 97 1n engagement with contacts 80, 100 and 99, respectively. g

When relay 66 was first energlzed, 1t prepared for the movement of arms 83, 246,63 and into engagement, respectively, with contact points 85,246, 65 and 71; and upon its de-energization, caused the engagement of the said arms with the said contact points. A reference to magnet 16, illustrated in Figure 1, and the method of operation of the sa d magnet in connection with ratchet 27, discloses a convenient mechanical combination by which the aforesaid movement may be effected.

The engagement of contact point by arm 83 put ground on contact 80 of the first selector switch and its multiples through relay 89, rendering the said switch busy with respect to other private switches having ac-. cess to it. The engagement of arm 246 with contact point 246 rendered the private switch of subscriber A busy with respect to other subscribers establishing connection with his line. The engagement of arms 63 and 70 with contact points 65 and 71, respectively, extended the limbs of the line of subscriber A throu h to the circuits of the first selector switch, thereby rendering the said switch controllable by subscriber A from the substation.

Subscriber A, by means of key 60, now grounds limb P of the line a number of times, corresponding to the thousands digit of the called subscribers number, or three times, causing three impulses of current to flow from ground at the substation, over limb P of the line, through contact 63-65, through common strip of his private switch, through wiper 98 to contact 100, throughicontact 101-102, through the winding of primary relay 104 to battery 74.

Each impulse of current causes an energization-and dc-energization of primary relay 104, which attracts and releases its armature three times and causes three impulses of current to flow from ground at the first I selector switch, through contact 108-109,

through contact 106-105, through the winding of primary magnet 114 to battery 74. The resulting energizations of primary magnet 114 cause three primary rotary movements of" shaft 132. The third movement brings wipers 129, 133 and 136 to positions adjacent to, but not engaging, the first contacts of three horizontal rows of contacts, multipled terminals of second selector switches assigned to the third one thousand line group of subscribers lines, or a group including lines of subscribers to whom are assigned numbers from 3000 to 3999.

Subscriber A new sends, by key 61, one impulse of current from ground at the substation, over limb S of the telephone line,

" through contact 70-71, through contact 99 -97-99, through contact 115-116, through the winding of secondary relay 118 to battery 74, causing a single attraction and release of the relays armature and a flow of current from ground, through contact 119-120, throughthe winding of C11- cuit-changing switch magnet 111 to battery 7 4. This causes the energization of the said magnet and the attraction of its armatures. The attraction of armature 108 causes a flow of current from ground, through contact 108-110, through the winding of secondary magnet 122 to battery 7 4. c The latter magnet is arranged in a vibratory circuit. Its

first energization and de-energization operates to move wipers 129, 133 and 136 into engagement With the first contacts of the rows described. In case these are terminals of a second selector switch already in use,

circuit-changing switch magnet 111 is main-' tery 74. The windings of relays 139 and 111 are so proportioned that this flow of current is not of suflicient volume to cause relay 139 to attract its armature. It is apparent that secondary magnet 122 will continue to vibrate, causing with each energization and ole-energization a secondary movement of shaft- 132, carrying with its wipers 129, 133 and 136 as long as magnet 111 continues energized. When wipe-rs 129, 133 and 136 engage contacts, terminals of an idle second selector switch, which is assumed to occur when they engage contacts 130, 131 and 137, terminals of second selector switch, Figure 3, contact 130 is insulated from ground and the flow of current through magnet 111 is interrupted. Its armaturcs thereupon resume their normal positions shown i-n the illustration, breaking contact 108-110 and preventing further operation of secondary magnet 122. Vipers 129, 133 and 136 are thus brought- -to rest in engagement with contacts 130, 134 and 137. The

dc-energization of circuit-changing switch magnet 111 also moved arms 126, 102 an-d 115, respectively, into engagement with contacts 128, 103 and 117, respectively. The closure of contact 126-128 put ground through relay 139, through contact 128-126, contact 131-129-130, to the multiples of contact 130, rendering the second selector switch busy with respect to other first selector switches having access to it. The closing of contacts 101-103 and 115-117 extended limbs P and S of the telephone line through to the circuits of the second selector switch, Figure 3, and rendered the said switch controllable from substation A.

Subscriber A now grounds limb P of his line a number of times, corresponding to the hundreds digit of the called subscriber's number, or four times, causing four impulses of current to flow from ground at the substation.-over limb P, through contact 3, through the windin 17 2. The fourth of these movements brings the wipers to positions adjacent to, but not engaging, rows of contacts, multipled terminals of connector switches assigned to a group of lines including subscribers lines which are assigned numbers from 400 to 499 of the selected one thousand.

Subscriber A now causes a single impulse of current to flow from ground at the substation, over limb S of the line, through contact 204-205 of the second selector switch, through secondary relay 207 to battery 149, causing a single attraction and re lease of the relays armature, and an im pulse of current to flow from ground at the second selector switch, through contact.

. 210-209, through the'winding of circuitchanging switch magnet 154 to battery 149. The consequent attraction of the magnets armatures established a flow of current from ground, through contact -152, through the winding of secondary magnet 157 to battery 149. Magnet 157 is placed in a vibratory circuit and will alternately be energized and de-energized until contact 150 152 is broken. Each-energization and (le'energization of magnet 157 causes a secondary rotary movement" of shaft 168, mov.-.

ing wipers 165, 169 and 172 to successive sets of contacts, term nals of connector switches of the described group, until ter-' ,minals of an idle. switch are reached. In

case contacts of the rows, engaged by wipers 165, 169 and 172, are terminals of a busy connector switch, magnet 154 is main-' tained energized by a flow of current from ground at the second selector switch then connected with the said connector switch, through relay 175, contact 162-164,,contact- 167-165 of the second selector switch referred to, to a multiple of the contact engaged by wiper 165 of Figure 3, to said contact, to common strip 167 of the second selector switch now being operated, through its contact 162-163," through contact 156- 155, through the winding of magnet 154 to battery 149. Such flow of current is of insufficient volume to-cause relay to attract its arn'iature. hen a contact, terminal of an idle connector switch, is reached by wiper 165, such contact will be insulated from ground and circuit through magnet 154 will be interrupted, tie-energizing it and thereby allowing thereturn of its armature to normal and preventing further energizations and de-energizations of secondary magnet 157; wipers 165, 169 and 172 resting in engagement, respectively, with contacts 166, 170 and 173, assumed to be terminals of a trunk line extending to "the selected connector switch shown in Figure 4. The de-energ'ization of circuit-changing switch magnet 154, above mentioned, also caused arms 162-, 142 .and 204 to move into engagement with contacts 164, 144 and 206, respectively. The closing of contact 162- 164 put ground to contact 166- and its multiples, rendering the said connector switch busy with respect to othersecond selector switches having access to it. The closing of contact 142-144 and contact 204-4206 extended limbs P and S of the telephone line of subscriber A'through to the circuits of the connector switch shown in Figure 4, rendering the said switch controllable from substation A.

Subscriber A now causes five impulses to flow from ground at the substation, Ck

through contact 171-169-170, contact 178-179, contact 181-182, contact 184- 185, and through the winding of primary relay 188 of the connector switch to battery 189. Five attractions and releases of said relays armature are caused thereby, resulting in five impulses of current flowing over the following path: from ground at the connector switch, through contact 192-191, through contact 195-194, through contact 198-199, through the winding of primary magnet 202 to battery 203. Each energiza- ,tion of'primary magnet 202 effects a primary rotary movement of shaft 239, carrying with it wipers 236,, 240 and 243. The fifth movement brings the wipers adjacent to rows of contacts, multipled terminals of the lines of subscribers'to whom are assigned numbers from 3451 to 3460.

Subscriber A now sends one impulse of current from ground at the substation, through -,contact- 174-172-173, through contact 211-212, contact 216-214, contact 217-218, through the Winding of relay 221 to battery 189. The resulting attraction and release of the relaysarmature causes an im pulse of current from ground, through contact 192-223, through the winding of circuit-changing switch magnet 193 to battery 189. The resulting energization and de-energization of magnet 193 operates to move arms 224, 198, 184, 217 and 228 into engagement with contacts 226, 200, 186, 219 and 230, respectively. The engagement of arm 198 with contact 200 places secondary magnet 233 under control of primary relay 188. Six impulses of current are now caused by subscriberA to flow'from ground at the substation, through contact 184-186 and primary relay 188,-Figure 4, to battery 189.

lit)

the relays armature causes a flow of current from ground, through contact 192191,

through contact 195-194, through contact 198200, through the winding of secondary magnet 233 to battery 203. Each energization and de-energization of the said secondary magnet causes wipers 236, 240 and 243 to move to engage successive contacts of the rows above mentioned, the sixth movement bringing the wipers into engagement, respectively, with contacts 237, 241 and 244, multipled terminals connected to the private switch of subscriber B, or subscriber 3456. Subscriber A now causes one impulse of current to flow from ground at the substation, through contact 217219 of the connector switch, through relay 221 to battery 189, causing circuit-changing switch magnet 193 to be energized by establishing a flow of current over the path previously traced.

Assuming first that the line of the called subscriber is busy, contact 237 in this case is characterized by a ground connection; and upon the attraction of armature 196 of magnet 193, closing contact 196-197, a flow of current results from grounded contact 237, through wiper 236, through common strip 238, through contact 224226, contact 197196, through the winding of release magnet 232 to battery 189, energizing magnet 232. When the impulse through relay 221 ceases, causing the de-energization of circuit-changing switch magnet 193, the latters armature 196 disengages anvil 197, opening circuit through release magnet 232, causing its de-energization and the consequent return of the connector switch to normal; wipers 236, 240 and 243 disengaging contacts 237, 241 and 244, and arms 224, 198, etc. returning to their normal engagement with contacts 225, 199, etc.

WVhen the connector switch returns to normal, contact 235234 is closed and the calling subscriber receives the busy signal from machine 263 in his receiver, notifying him that the line called is busy. He thereupon simultaneously presses keys 60 and 61 and replaces his receiver. Relays 188 and 221 of the connector switch, Figure 4 are simultaneously energized, closing contact 190 222, establishing a path for the flow of current as follows: from ground at second selector switch, Figure 3, through release relay 175, through contact 164162, through contact 167165166, through contact 251250 (Figure 3), through contact 190 222 (Figure 4), through the winding of release magnet 232 to the active side of battery 189. This flow of current energizes release relay 175 of Figure 3, and release magnet 232 of Figure 4. The energization of release relay 175 operates to prepare the second selector switch, Figure 3. first selector switch, Figure 2, and private switch, Figure 2 for their returns to normal. which will occur as soon as subscriber A releases keys '60 and 61, thereby removi' ig ground from the limbs of the line, which causes the deenergizationof relays 188 and 221 of Figure 4, and the opening of contact 222190. The opening of this contact causes the de-energization of release relay 175. The detailed description of the manner in which release relay 175 operates in connection with the returns to normal of the various switches will be hereinafter given.

In case the line of subsctiber B is idle, contact 237 is connected to battery through relay 266, and release magnet 232 does not become energized upon the closure of contact 196-197. In this case, the energization and de-energization of circuit changing switch-magnet 193 operates tomove arms 224, 198, 184, 217 and 228 into engagement, respectively, with contacts 227, 201, 187, 220 and 231. The engagement of arm 224 with contact 227 places ground upon contact 237 and its multiples, rendering the said line of subscriber B busy with respect to other subscribers establishing connection with it. It also energizes relay 266 of the private switch which operates to cut limbs P and S of the line of subscriber B free from the circuits of the private switch. The engagement of arm 228 with contact point 231 establishes a path for the flow'of current as follows: from ground at battery control circuit, Figure 3, through the winding of relay 247, through contact 231-228 of the connector, switch, through the winding of release magnet 232 to battery 189, causing the energization of relay 247. The windings of magnet 232 and relay 247 are so proportioned that this flow of current does not cause the energization of magnet 232' to a degree to cause it to attract its armature.

It will be observed that the structure of Fig. 1 does not provide for a second forward movement of circuit-changing switchmembers as described for arms 224, 198, 184, 217 and 228. For this purpose the well known side switch escapement movement, shown and described in Patent #815,321, dated March '13, 1906, to Keith et a]. maybe conveniently employed, magnet 193 controlling the forward stopping of the side switch arms, while release magnet 232 when de-energized restores the side switch arms, all as described in the patentcited.

The energization of relay 247 operates to close the following contacts: 17 8180, 182-183, 211213 and 214215. of current new results over the following path: from the grounded side of battery 256, through the lower winding, as illustrated, of relay 255, through relay 252, enerzizinsz the said relav and attractine its A flow of ringing relay 257 to battery 256.

armature, through contact 213211, through contact 173172-1'Z4, over the talking circuit as shown by the heavy lines, by way of limb S of the line of subscriber A, through the substation; supplying current to the transmitter for talking purposes, returning over limb P, the other side of the talking circuit through the exchange, through contact 171.169170, contact 178180, impedance coil 263, through the upper Windingpf relay 255, to the active side of'battery 256. This flow of current does not cause relay 255 to attract its armature, the said relay being differentially Wound.

To cause .the bell of subscriber B to be rung, subscriber A opens the path of the just-traced flow of current at his substation by means of key 62. This causes the dc-energization of relay 252, its armature assumes the position shown in the illustration (Figure 3), closing contact 253254 and estab lishing a path for the flow of current from ground (Figure 3), through contact 249 248, contact 253-254, through the win%iln g 11s energizes the said relay, it attracts its armatures and cuts ringing generator 258, by the said attraction, into circuit with the line of subscriber B, causing his bell to ring. When subscriber A releases key 62, the talking current resumes its flow through the substation, relay 252 is again energized, the attraction of its armature breaking circuit through ringing relay 257, whose armatures resume their normal positions as shown in Figure 3.

When subscriber B answers the call by removing his receiver from the hook, contact 72-73 is closed, and a flow of current results from the grounded side of battery 256 (Figure 3), through impedance 265, over the talking circuit at the exchange, as shown by the heavy lines, to limb S of the line of subscriber B, through the substation, supplying currcnt to the transmitter, returning over limb P of the line, over the talking circuit, through impedance 264-to the active side of battery 256. The two subscribers are now in conversation through condensers 261 and 262, the conversational circuit being traced through the exchange by the heavily lined conductors.

lVhen the subscribers have finished their conversation, each depresses simultaneously keys 60 and 61 and replaces his receiver upon the switch hook. Assuming that subscriber B does this first, the release of the apparatus used in establishing the connection between the two subscribers is secured in the following manner: The grounding of limb S by subscriber B short circuits-the lower winding of relay 255 .of Figure 3;

while the grounding of limb P maintains-- the flow of current through the upper winding of relay 255 from the ac'tiveside of battery 256, over limb P to ground at the substation. Rcla'y 255 is ditferentially wound, and the flow of currentthrough its two windings during conversation and before did not cause the attraction of'armature 259.

The short circuiting of the lower Windin as above described, current continuingito in the upper windlng, causes the magnetiza tion of the core of relay 255 and the attraction of its armature 259 to engage anvil 260. A flow of current is thereby caused over the following path: from ground, Figure 3,

the connector switch, Figure 4, to normal upon the de-energization of the said magnet. The attraction of the armature of the release relay'17 5 establishes a path for the flow of current as follows: from ground, Figure 2, through the winding of release relay 139, through contact 128126, through contact 131129-130, through contact 177-17 6, through the winding of release magnet 161 to battery 149, causing the attraction of the armatures of relay 139 and magnet 161; The attraction of the armature of magnet 161 prepares for the release of the' second selector switch, Figure 4, and its return to normal upon the de-energization of the magnet. The energization of relay 139 establishes a path for the flow of current as follows: from ground at the private switch, Figure 2, through the winding of relay 89, through contact 85-83, through contact 7982'80, through contact 141- 140, through the winding of release magnet llt 125 to battery 74, the resulting energization of magnet 125 preparing for the release of the first selector switch, Figure 3, and its return to normal upon the de-cnergization of the said magnet. The energization of relay 89, which results from the above described flow of current, causes a flow of our rent as follows: from ground atthe private switch,'through contact 8688, through the winding of relay 66 to battery 74, and the energization of thesaid relay.

hensubscriber B releases keys 60 and 61, they returnto their normal positions as shown; assuming that subscriber 'A has not yet depressed.keys GO'and 61 at his substation, relay 255 no longer-attractsa-rmatu-re 259, and the said armaturedlsengages" anvil 260. 'This causesthefde energiz'a'tion of releaseunagnet 232' of thefl'connector' switch, Figure 4, and the return of the switch to normal. I The return of arm 228 of this switch opens the circuit of relay 247 of Figure 3. Its consequent .de-energization causes rel.

and the release of its armatures causes arms 178, 211, 182 and 214 to return to normal. The release of the connector switch also 266 of private switch, Figure 4, to become e-energized, restoring the private switch to normal. The de-energization of release relay 175 of the second selector switch, Figure 3, is caused by armature 259 disengaging anvil 260. The resulting openzation of relay 66 and the return of arms 83, 246, 63 and 70 to their normal positions as shown in the illustration. It is to be understood that the release of the private switch, or its return to normal, consists in the above described operation only, wipers 82, 98 and 97 remaining in engagement with terminals of the first selector switch used. The return of arm 83 to its normal engagement with its contact 84 removes ground from contact 80 and its multiples, rendering the first selector switch, Figure 2, idle with respect to other private switches having access to it.

Should subscriber A depress keys and i61 at his substation and replace his receiver before subscriber B does so, the grounding of limb S of the line of subscriber A short circuits the lower winding of relay 255, current continuing to flow through the upper winding, over imb P, to ground-at the substation. The core of the relay is thereupon magnetized, armature 259 engages anvil 260, and the release operations proceed exactly as described in the case in which subscriber B performs the release operation at his substation first. 7

It will be noted that during conversation, current flows through differentially wound relay 255 and in parallel paths over the lines of the two connected subscribers; that when one subscriber releases in advance of the other, current through the upper winding of relay 255 is of equal or of greater volume than that during conversation; while current through the lower winding is reduced approximatel one-half, the degree depending upon the comparative resistance of the two subscribers lines.

Q Should the two subscribers release simul- I tancously, the flow of current. through the upper winding of relay 255 will be substantially the same as that existing during conversation, while the flow of current through the lower winding will be practically nil.

A second complete diagram, illustrative of an alternate form of the circuits of the telephone system of my invention, comprises Fig. 2,-Fig. 5 and Fig. 4, placed .in the order named. The method of operation of this circuit is largely the same as that of the circuit diagram already described, the ditierence existing in the battery control circuit, Figure 5. The said Figure 5 provides means whereby, upon the response of the called subscriber, the direction of the flow of current in the line of subscriber A is reversed.

The description already given in connection with the previous circuit diagram applies to this second diagram to the point at which wipers 165, 169 and 172 of the second selector switch come to rest in engagement with contacts 166, 170 and 173. The impulses sent over limb P of the line, corresponding to the tens digit of the called subscribers number, after passing through contact 171169170, in this case pass through contact 270-271, through contact 301300 and through the winding of pri mary relay 188, operating the connector switch of Figure 4 in the manner already described. The single impulse sent over limb S of'the line after the just mentioned set of primary impulses, after passing through contact 174172-173, passes through contact 27 3274, contact 305303- and through the winding of relay 221. The impulses corresponding to the units digit sent over limb P, and the single impulse sent over limb S thereafter, traverse the above described paths.

The releaseof the connector switch, in case the line of the called subscriber is busy, is secure in the same manner as described in connection with the preceding diagram. Should the line of subscriber B be idle, arms 224, 198, 184, 217 and 228 are caused to engage contacts 227, 201', 187, 220 and 231, as in the preceding description. The engagement of arm 228 with contact point 231 establishes a path for the flow of current from ground at battery control circuit, Figure 5, through the winding of relay 276, causing its energization, through contact 231-228, through the winding of release magnet 232, which, due to the resistance of relay 276, does not attract its armature, and to battery 189.

The energization of relay 276 (Figure 5) causes the attraction of armatures 277 and 279, and causes arms 270,273. 300 and 303 to engage contact points 272, 275, 302 and 304, respectively.

Current thereupon flows as follows: from the grounded side of battery 287, through the lower winding of differentially-wound relay 284, through the lower winding of relay 281, through contact 293294, through over limb P, over the talking circuit,

through contact 270272, through contact 296295, through the upper winding of relay 281, through the upper winding of relay 284, to the active side of battery 287 The coreof relay 284 is not magnetized by this flow of current, owing to its differential windings. The core of .relay- 281 is energized, attracting its armature 283 to open contact 282-283. Subscriber A o ens the path o f the previously traced flow 0 current by means of key 62, causing the de-energization of relay 281,'armature 283 falling back to establish a path for the flow of current as follows: from ground, through contact 282-283, through contact 280279, through the windin of ringing relay 288 to the active side of battery 287. Relay 288 attracts its armatures, cutting ringing generator 289 into circuit with the called-for subscribers line and causing his bell to ring. When subscriber releases ringing key 62, it closes circuit'through the substation, relay 281 is again energized, opening contact 282-283, de-energizing relay 288 and allowing the said relays armatures to resume their normal positions. \Vhen subscriber B, in response to the call, removes his receiver from the hook and closes contact 7372, an additional path for the flow of current, from battery 287, is established as follows: from the grounded side of the said battery, through the lower winding of relay 284, through winding 292 of relay 290, through contact 304 -303, over the talking circuit at the exchange, to limb S of the line of subscriber B, through the substation, returning over limb P, over the talking circuit, through contact 300-302, through winding 2910f relay 290, through the upper winding of relay 284 to the active side of battery 287. This flow of current causes theenergization of relay 290, attracting its armatures to close contacts 294295 and 296-297, contacts 293-294 and 295-296 being opened. The original flowv of current, from'battery 287 over the line of subscriber A, was from the grounded side of the said battery, over limb S, returning by way of limb I? to the active side of the said battery. The attraction of the armatures of relay 290 reverses the direction of this flow of current, the path now being traced from the grounded side of battery 287, over limb, P ofthe line, returning over limb S to the active side of the battery.

While the provision of means .for reversing the direction oftheflow of current in the calling subscribers line, upon the response of the called-for subscriber, is not essential to the operation of the system as shown, the feature is of value as rendering the system of the whole more flexible, being adapted to be used for various signaling purposes in connection with polarized electromagnets. An example of structures such as may be used in connection with the present system is shown in Fig. 5 of Patent 830,653 to A. H. Dyson issued Sept. 11, 1906.

When, at the conclusion of the conversation, either subscriber depresses keys 60 and 61 to round the limbs of his line and replaces is receiver, the neutralizing effect of 1ts two windings upon the core of differentially-wound relay 284 is unbalanced; armature 285 is attracted to engage anvil 286, es-

vtablishing a path for the flow of current from ground at the second selector switch, Figure 5, through the winding of release relay 175, through contact 164-162, through contact 167165-166, contact 285-286, then joining the flow from ground through relay 276, through contact 23 1228, through the winding of release magnet 232 of the connector switch, Figure 4, to battery 189, causing the energization of release magnet 232 and release relay 175 of the second selector switch, Fi ure 5. Relay 276 of the battery control clrcuit, Figure 5, continues energized under these conditions. The energizations of the release magnets of the second selector switch, first selector switch and the private switch are accomplished in the same manner as described in connection with the .first complete circuit diagram. When the releasing subscriber removes ground from the two limbs of his line at the substation, armature 285 of relay 284 (Figure 5) disengages anvil 286 and opens circuit through release relay 175 of the second selector switch, Figure 5, and release magnet 232 of the connector switch, Figure 4, causing their (le-energizations. The leenergization of release magnet 232 causes the return of the connector switch, Figure 4, to normal; the opening of contact 231 228, caused thereby, breaks the circuit. through relay 276 of the battery control circuit, Figure 5, de-energiz'ing it, arms 270, 273, 300 and 303 thereupon returning to normal. The return to normal of the second selector switch, first selector switch and the rivate switch are accomplished as described In connection with the first complete circuit 0 diagram. D

A third complete, diagram, lllustrative of the circuit of my invention for prov ding means whereby subscribers whose lines ter-' minatein different exchanges may automatically interconnect their llnes, two conductors only being required for a trunk crrcuit between exchanges, com rises Fig.2, Fig. 6, Fig. 5 and ,Fig. 4 place 1n the order named with Fig. 6 superposed upon Flg. 5 so that the left portion of Fig. *5 Including contacts lit) 166, 170 and 173 is covered by Fig. 6. p and s are the two limbs of a trunk circuit; the apparatus in this diagram to their left being assumedjo be in one exchange, and that to their right in the second exchange. The method of operation of this circuit is similar to those already described to the point at which wipers 129, 133 and 136 of the first selector switch, Figure 2, come to rest; in engagement with contacts 130, 134 and 137. Imp-ulses corresponding to the hundreds digit ofv the called subscribers number, sent by subscribemA from ground at the substation, pass through contact 135- 133-134, throu h contact 306-307, through the winding 0? primary trunk relay 309, to battery 321. These four impulses of current cause four attractions and releases of the armature of relay 309, each attraction and release causing an impulse of current to flow .as follows: from ground at Figure 6, through contact 313-312, through contact 348-347, over limb p of the trunk line, through contact 142-143, through the winding of primary relay 145 of the trunking second selector switch, Figure 6. The four attractions and releases of the armature of relay 145, caused by the above mentioned impulses of current, cause four impulses of current to flow from ground at the second selector switch, Figure 6, through contact 150-151: through contact 148-147, through the winding of primary magnet 153 to battery 149, causing four primary movements of shaft 168 and themovement of wipers 165, 169 and 172 to positions adjacent to, but. not engaging, levelsof contacts, terminals of connector switches assigned to the four hundreds group of the third thousand. The calling subscriber now causes one impulse of current to flow from ground at the substation, over limb S of the line, through contact 138-136-137, through contact 318-319, through the winding of secondary trunk relay 317 to battery 321, causing the attraction and release of the armature of said relay and an impulse of current to flow from ground, through contact 313-314, through contact 351-350, over limb s of the trunk line, throughcontact 204-205, through the'winding of secondary relay 207 to battery 149. The resulting attraction and release of the relays armature causes an impulse of current to flow from ground at Figure 6, through contact 210-209, through the winding of circuit-changing switch magnet 154 to battery 149, causing the energization of the magnet and the attraction of its armatures. The closing of contact 150-152 causes a flow of current from ground, through the said contact, through the winding of secondary magnet 157 to battery 149. Wipers 165, 169 and 172 move over the contacts of the before-mentioned levels, terminals of busy connector switches being grounded, as described in connection with the previous diagrams, and maintaining the circuit-changing switch magnet energized. When the wipers reach contacts, terminals of an idle connector switch, circuit-changing switch magnet 154 is tie-energized, opening circuit through secondary magnet 157 and preventin further movement of the wipers under t e influence of the said magnet. At the same time, it moves arms 162, 142 and 204 into engagement with contact points 164, 144 and 206, respectively.

The impulses sent from ground by subscriber A, corresponding to the tens digit of the called subscribers number, cause five energizations and de-energizations of primary trunk relay 309, resulting in five impulses flowing over the following .path; from ground, through contact 313-312, contact 348-347, over limb p of the trunk line, through contact 142-144, contact 171 169-170, contact 270-271, contact 301- 300, contact 184-185, through the winding of primary relay 188 and to battery 189. The resultin energizations and de-energizations of re ay 188 cause the operation of the connector switch as described in connection with the preceding complete diagrams. The impulse of current, sent by subscriber A from ground at the substation, over limb S of the line, passes through secondary trunk relay 317, over the previously traced path. Theenergization and de-energization of this relay causes an impulse of current 100 i to flow from ground, through contact 313-314, through contact 351-350, over limb s of the trunk line, through contact 204-206, contact 174-172-173, contact 273-274, contact 305-303, contact 217-218, through the winding of relay 221 to battery 189. Relay 221 operates the connector switch, as previously described. The six impulses corresponding to the units digit of the called subscribers number, sent by subscriber A over limb P of the line, and a single impulse, following the six'sentover limb S, are transmitted by relays 309 and 317 of Figure 6 to relays 188 and 221 of the connector switch, Figure 4, over the previously traced paths, causing Wipe1s 236, 240 and 243 to engage terminals of thecalled subscribers line.

Should the line be busy, the connector switch is released and subscriber A receives the busy signal fr, m busy-back machine 263, as previously described.

Should the line be idle, the engagement of arm 228 with contact 231 causes a flow of current from ground at battery control circuit, Figure 5, through relay 276, contact 231-228 and release magnet 232 to battery 189, the latter magnet not being operated thereby. The a-rmatures of relay 276 are attracted, and arms 270, 273, 300 and .303 l battery 287 through engage, respectively, contacts 273, 275, 302- and 304. Current thereupon flows from the grounded side of battery 287 through a Winding of relay 284, a winding of relay 281, through contact 293-294, through contact 275-273, through contact 173-172- 174, through contact 206-204, over lZimb -s of the trunk circuit, contact 350-351, contact 314-315, through the winding of relay 322, through contact 311-312, through contact 348-347, over limb p of the trunk line, through contact 142-144, through contact 171-169-170, contact 27 0-272, through contact 296-295, the upper winding of re lay 281, the upper winding of relay 284, to the active side of battery 287. This flow of current energizes relay 322 of Figure 6, its armature being attracted to close contact 324-323. Current then flows from ground, through the said contact, through contact 327-326, through the winding of magnet 325 to the active side of battery 321. Magnet 325 is energized and its armature is at.-

.tracted, preparing to move arms 306, 318,

347 and 350 into engagement with contacts 308, 320, 349 and 352 upon its de-energization. As the armature is attracted, it opens the magnets circuit; the armature thereupon drops back, and arms 306, 318, 347 and 350 are moved, respectively, into engagement with contact points 308, 320,349 and 352. Pawl 21, associated with magnet 16; in F igure 1, and ratchets 26 and 27 with their circuit-changing arrangement, comprise a me-' chanical combination that may be employed in connection with magnet 325. The closing of contacts 306-308 and 318-320 establishes a path for the flow of current from the grounded side of battery 328, through the lower windings of relays 329 and 334, through contact 341-340, through contact 320-318, over the talking circuit at theexchange,to limb S of the line of substation A, through the substation, returning over .limb P, the talking circuit contact 306-308,

through contact 337-338, through the upper windings of relays 334 and 329, to the active side of battery 328. Relay 329 is differentially wound, and themagnetic effects of itstWO windings upon its core are balanced. Relay 334 is not differentially wound; its core is energized and attracts armature 335 to engageanvil 336. Current thereupon'fiows from the groundedside of contact 275-273, through contact 173-172-174, through contact 206-204, through contact 350-352, contact 335-336, through the two windings of polarized electromagnet 343 in series, through contact 349-347, through contact 142-144, contact 171-169-170, through contact 270-272, and to the active side of battery 287. This flow of current 'is in a d rection such that polarized electromagnet ing contact 336-335, which interrupts the flow of current through rlay 281 (Figure 5), de-energizing the said relay and allowing armature 283 to engage anvil 282. The closing] of contact 283-282 closes circuit through ringing relay 288, causing it to attract its armatures and include generator 289 in circuit with the called subscribers line, ringing the substation bell. Whensubscriber A releases key 62, closing circuit through the substation, relay 334 of Figure 6 is again energized, its. armature is attracted, closing contact 335-336, and current again flows through relay 281 (Figure 5), causing it to attract its armature and open the circuit of ringing relay 288, whose armatures return to normal.

When the called subscriber B answers the call by removing his receiver from the hook, contact 73-72 is closed, establishing a path for the flow of current from the grounded side of battery 287, through winding 292 of relay 290, over limb S, through the substation, returning over limb P and through winding 291 of relay 290, to the active side of battery 287, energizing relay 290. The energization of this relay, as described in connection with the second circuit diagram, reverses the connections of battery 287 to the talking circuit on the calling subscribers side of condensers 298 and 299. In this case, the direction of the flow of current from battery 287, through the windings of polarized relay 343 of Figure 6, is reversed, the said relay is actuated, and its armature 344attracted, closing contacts 342-340 and 339-337, and opening contacts 341-340 and tioned reverses the direction of the flow -of current from battery 328, over the line of the calling subscriber A. v

The two subscribers are now in conversa- -tion through condensers 298 and 299,'fover limbs 79 and 8 of. the trunk circuit, and through condensers 345 and 346.

When the subscribers have finished their conversation, they. depress keys 60 and .61 and replace their receivers as before. As; suming that subscriber A does this first, the grounding of limb P of the line at the substation short circuits thelower winding of differentially Wound relay 329 (Figure 6) while current continues to flow in equal, J 

